Rotating machines, such as turbines, compressors, and compact motor-compressors, are often utilized in a variety of applications and industries to compress a gas. FIG. 1 illustrates a partial cross-sectional schematic view of a conventional rotating machine 100. The conventional rotating machine 100 may include a motor 102 coupled with a compressor 104, such as a centrifugal compressor, in a hermetically sealed housing 106. Through a rotary shaft 110 supported by one or more bearings 108, the motor 102 may drive or rotate the compressor 104 in order to generate a flow of a compressed process gas. As illustrated in FIG. 1, the bearings 108 may be utilized at various positions along the rotary shaft 110 of the rotating machine 100. For example, the bearings 108 may be positioned at or near one or more axial ends of the rotary shaft 110 and, depending on a length of the rotary shaft 110, at one or more positions between the axial ends of the rotary shaft 110. As the motor 102 drives the compressor 104, heat may be generated along the rotary shaft 110 at interfacing surfaces between the rotary shaft 110 and the bearings 108. At high rotational speeds, the temperature of the rotary shaft 110 at and/or about the interfacing surfaces may be higher than other portions of the rotary shaft 110, resulting in non-uniform heating along the length and/or around a circumference of the rotary shaft 110. The non-uniform heating may cause the rotary shaft 110 to bend at these interfacing surfaces, thereby causing synchronous instability and/or vibration of the rotary shaft 110. The synchronous instability and/or vibration of the rotary shaft 110 may decrease the efficiency of the rotating machine 100 and/or cause damage to one or more components thereof.
In view of the foregoing, rotating machines 100 often minimize synchronous vibrations by reducing the rotational speed of the rotary shaft 110. Reducing the rotation speed, however, limits the production capacity of the rotating machine 100. Further, reducing the rotational speed may not be a viable option where the motor 102 of the rotating machine 100 lacks a variable frequency drive.
What is needed, then, is a rotary shaft and method for reducing non-uniform heating thereof, capable of minimizing synchronous vibrations by reducing or diffusing heat localized at and/or about the interfacing surfaces between the rotary shaft and bearings of a rotating machine.